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Re: [PATCH v3 0/2] hw/nvme: Add shadow doorbell buffer support
From: |
Klaus Jensen |
Subject: |
Re: [PATCH v3 0/2] hw/nvme: Add shadow doorbell buffer support |
Date: |
Mon, 27 Jun 2022 08:00:13 +0200 |
On Jun 16 20:34, Jinhao Fan wrote:
> This patch adds shadow doorbell buffer support in NVMe 1.3 to QEMU
> NVMe. The Doorbell Buffer Config admin command is implemented for the
> guest to enable shadow doobell buffer. When this feature is enabled, each
> SQ/CQ is associated with two buffers, i.e., Shadow Doorbell buffer and
> EventIdx buffer. According to the Spec, each queue's doorbell register
> is only updated when the Shadow Doorbell buffer value changes from being
> less than or equal to the value of the corresponding EventIdx buffer
> entry to being greater than that value. Therefore, the number of MMIO's
> on the doorbell registers is greatly reduced.
>
> This patch is adapted from Huaicheng Li's patch[1] in 2018.
>
> [1]
> https://patchwork.kernel.org/project/qemu-devel/patch/20180305194906.GA3630@gmail.com/
>
> IOPS comparison with FIO:
>
> iodepth 1 2 4 8
> QEMU 25.1k 25.9k 24.5k 24.0k
> +dbbuf 29.1k 60.1k 99.8k 82.5k
>
> MMIO's per IO measured by perf-kvm:
>
> iodepth 1 2 4 8
> QEMU 2.01 1.99 1.99 1.99
> +dbbuf 1.00 0.52 0.27 0.46
>
> The tests are done on Ubuntu 22.04 with 5.15.0-33 kernel with Intel(R)
> Xeon(R) Gold 6248R CPU @ 3.00GHz.
>
> QEMU set up:
>
> bin/x86_64-softmmu/qemu-system-x86_64 \
> -name "nvme-test" \
> -machine accel=kvm \
> -cpu host \
> -smp 4 \
> -m 8G \
> -daemonize \
> -device virtio-scsi-pci,id=scsi0 \
> -device scsi-hd,drive=hd0 \
> -drive
> file=$OSIMGF,if=none,aio=native,cache=none,format=qcow2,id=hd0,snapshot=on \
> -drive "id=nvm,if=none,file=null-co://,file.read-zeroes=on,format=raw" \
> -device nvme,serial=deadbeef,drive=nvm \
> -net user,hostfwd=tcp::8080-:22 \
> -net nic,model=virtio
>
> FIO configuration:
>
> [global]
> ioengine=libaio
> filename=/dev/nvme0n1
> thread=1
> group_reporting=1
> direct=1
> verify=0
> time_based=1
> ramp_time=0
> runtime=30
> ;size=1G
> ;iodepth=1
> rw=randread
> bs=4k
>
> [test]
> numjobs=1
>
> Changes since v2:
> - Do not ignore admin queue updates in nvme_process_db and nvme_post_cqes
> - Calculate db_addr and ei_addr in hard-coded way
>
> Changes since v1:
> - Add compatibility with hosts that do not use admin queue shadow doorbell
>
> Jinhao Fan (2):
> hw/nvme: Implement shadow doorbell buffer support
> hw/nvme: Add trace events for shadow doorbell buffer
>
> hw/nvme/ctrl.c | 118 ++++++++++++++++++++++++++++++++++++++++++-
> hw/nvme/nvme.h | 8 +++
> hw/nvme/trace-events | 5 ++
> include/block/nvme.h | 2 +
> 4 files changed, 132 insertions(+), 1 deletion(-)
>
> --
> 2.25.1
>
>
Jinhao,
Thanks, applied to nvme-next!
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